1. Field of the Invention.
The invention relates generally to wellhead apparatus for receiving coiled tubing and, more particularly, but not by way of limitation, it relates to improved tubing hanger apparatus in combination with a hydraulically actuated double packer configuration.
2. Description of the Prior Art
The prior art includes numerous types of tubing hanger assembly that have been largely restricted to the mechanical fastener types that use slips or clamping jaws to hold the tubing rigidly at a predetermined position in the annulus of a wellbore. U.S. Pat. Nos. 3,675,719; 3,690,381; and 3,692,107 in the name of Slator et al. are directed to a pair of semi-circular gripping and support members which are suitably clamped about a tubing at a designated position and maintained clamped with upward directed clamping teeth securing the tubing. A circular array of threaded rods then serve to maintain clamping pressure to retain the tubing, and such threaded rods are accessible from outside of the hanger assembly at the wellhead position. There are many variations on such mechanical hanger assembly and these are shown and described in the patents cited in the Information Disclosure Statement.
More recent hanger assemblies function by using a circumfery of downwardly directed slips which define a circular bore having upwardly directed teeth, which slips rest on an inwardly directed surface inclined to contact with the coiled tubing. Such assemblies are known as threaded coiled tubing hangers and function by turning an upper hanger section relative to a lower hanger section thereby to force the circumfery of slips downward and inward around the tubing until sufficient hanging grip is exerted. A still more recent coiled tubing hanger is termed the SAFESET.TM. coiled tubing hanger as manufactured by Pedcor of Houston, Tex. This hanger includes a body assembly with axial passage for tubing insertion whereupon a circumfery of slip activation screws are rotated to move the slips downward and inward to a position adjacent the tubing in gripping relationship. Simultaneously, as the slips move downward and inward, they bear against a slip support cup adjacent the central bore which, in turn, compresses a packer element to expand inward into contact with the tubing thereby to seal off the annulus immediately around the coiled tubing.